keV Ion Beam Research Articles

Tailoring of keV-Ion Beams by Image Charge when Transmitting through Rhombic and Rectangular Shaped Nanocapillaries

We report on an unexpected effect of tailoring transmission profiles of Ne(7+) ions through nanocapillaries of rhombic and rectangular cross sections in mica. We find that capillaries of rhombic cross sections produce rectangular shaped ion transmission profiles and, vice versa, that capillaries of rectangular geometry give a rhombic beam shape. This shaping effect only occurs for transmitted ions and is absent for the small fraction of neutralized particles. The experimental findings and simulations of the projectile trajectories give clear evidence that the observed effect is due to the image forces experienced by the transmitting ions. This novel beam shaping mechanism suggests applications for the guiding, focusing, and shaping of ion beams.

Creation of self-organized gold nanostructures by keV ion beam irradiation

We synthesized Au nanostructures on glass by low-energy ion irradiation of a thin Au film. The Au films, deposited on a glass substrate, were irradiated by 50 keV Si− ions with different fluences. The UV–vis absorption spectroscopy of irradiated samples indicates the surface plasmon resonance peak, which is a signature of the formation of Au nanostructures. The surface morphology of the films has been characterized by atomic force microscopy, which supports the UV–vis spectroscopy findings. The metal content or the film thickness of the samples, as measured by Rutherford backscattering spectroscopy, decreased with increasing fluence, showing sputtering by ion irradiation and tailing in the lower energy edge with irradiation, revealing recoil implantation. The formation of Au nanostructures by this method can be explained on the basis of an interplay between surface instability due to ion beam sputtering and surface diffusion.

Nanopatterning of ZnS thin film surfaces by keV ion beam irradiation

The nanopatterning of crystalline ZnS thin film surfaces under 80keV Ar+ ions irradiation at incident angles of 0°, 20°, and 40° is presented. Structural and morphological changes have been investigated by means of X-ray diffraction and atomic force microscopy respectively. The surface morphology mainly consists of nanograins of spherical shape in pristine and films irradiated at normal incidence. The irradiation at oblique angle (20° and 40°) leads to the formation of ripple structures on the surface with a wave vector parallel to the ion beam direction. The existing theories for the ripple formation are invoked to explain the observed surface structure.

Effect of surface morphology of metallic zinc films deposited by ion beam sputter deposition on the formation of ZnO nanowires

Metallic zinc film with various surface roughnesses was deposited on Si (100) substrates by ion beam sputter deposition utilizing beam energies at 8, 12 and 16 keV. The surface roughness of the metallic zinc film increased as ion beam energy increased and was found to act as a crucial factor for the formation of ZnO nanowires by subsequent thermal oxidation. ZnO nanowires with diameters of ∼30 nm and average length of ∼1 μm were obtained from 12 to 16 keV ion beam deposited samples while no ZnO nanowires were found on 8 keV ion beam deposited samples. Photoluminescence study of ZnO nanowires exhibits a strong UV emission at 377.2 nm (3.287 eV) with a full-width at half maximum of 95.0 meV and negligible defect related deep level emission. The ZnO nanowires are grown along the [110] direction and the growth mechanism is likely due to a solid state based-up diffusion process. Field-emission measurement shows a turn-on field of 7.9 MV/m and a field enhancement factor β of 691 is achieved.

A narrow-band, variable energy ion source derived from a wire plasma source

A low pressure wire-induced plasma source (WIPS) operated in its high-pressure mode (∼10−2 mbar) exhibits a narrow ion energy distribution function peaked at an energy corresponding to the discharge voltage. In order to take advantage of this peculiar feature, we design an electrode geometry enabling the acceleration of ions extracted from a WIPS. Probing of the obtained ion plume by means of a retarding potential analyser (RPA) demonstrates the capability of such an ion source to generate narrow-band (full width at half maximum of about 20 eV), variable energy (1 to 5 keV) ion beams. Comparison with particle-in-cell simulations of the WIPS shows that the energy spread of these ion beams is actually about 10 eV, the slight broadening being mainly the effect of the limited planar RPA energy resolution. The ion beam spot size measured at 6 cm of the ion source exit is about 3 mm for a 10 µA He+ beam at 2 keV, with a divergence of about one degree. Operating the WIPS in argon and xenon leads to similar properties for Ar+ and Xe+ beams, and in principle other species could also be used.

Comparison of MeV monomer ion and keV cluster ToF‐SIMS

AbstractRecent results1 show the potential of using monomer primary ions accelerated to several MeV with a tandem accelerator to achieve the necessary secondary ion yields to image large (above 1 kDa) molecules with submicron lateral resolutions. The Surrey ion Beam Centre (Surrey IBC) has designed a time‐of‐flight secondary ion mass spectrometer (ToF‐SIMS) combined with a 2 MV Tandem accelerator to investigate the characteristics of the desorption of secondary ions by the impact of fast, heavy, primary ions. The application of this MeV‐ToF‐SIMS technique is intended to eventually image biomolecules in the subcellular regime without the need for matrix application associated with other mass spectromery techniques, such as Matrix Assisted Laser Desorption ionisation (MALDI). A discussion is given to point out the merits of using a combination of Particle‐Induced X‐ray Emission Spectrometry (PIXE) and Rutherford Backscattering (RBS) with the MeV‐ToF‐SIMS measurement to improve quantification and sensitivity of this surface analysis technique. We also present data from highly focused MeV primary ions to directly compare results obtained using keV cluster‐SIMS to measure various biological materials using ToF‐SIMS through sputtering in both the nuclear and electronic stopping regimes. Our findings show that the mass spectra obtained with MeV ions in the electronic stopping regime show similarities to those acquired with more conventional keV ion beams (e.g. Bi+, Bi3+, Bi5+ and C60+). MeV‐ToF‐SIMS has the potential for becoming a widely used quantitative surface analysis technique in the many ion beam analysis facilities already conducting‐high energy ion beam analyses. Copyright © 2010 John Wiley & Sons, Ltd.

Investigation of Damage Mechanisms in PMMA during ToF-SIMS Depth Profiling with 5 and 8 keV SF5+ Primary Ions

Cluster secondary ion mass spectrometry (cluster SIMS) has been proven to be a useful technique for the surface and in-depth characterization of molecular films. In this study, an SF5+ polyatomic primary ion source is utilized for depth profiling in poly(methyl methacrylate) (PMMA) bulk and thin films (200 nm). The effects of SF5+ ion beam energy are discussed in detail. Both 5 and 8 keV ion beam energies are utilized for depth profiling experiments, where the chemistry of sputtering is investigated using surface analytical tools such as X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) in conjunction with SIMS. Thin film depth profiles acquired with 5 keV SF5+ display evidence of significant damage accumulation at the interface in the form of a highly cross-linked polymer gel. There is very little evidence of similar damage accumulation at the interface for the corresponding 8 keV SF5+depth profile. AFM and XPS analysis of the sputtered crater bottoms also indicates that very different chemistries and morphologies are present at the interface when employing 5 keV vs 8 keV SF5+. For PMMA bulk samples, greater erosion depths were achieved when employing higher beam energies, similar to what has been observed previously with C60n+ depth profiling.(1) These increased erosion depths are attributed to the increased sputter rates of the PMMA at 8 keV SF5+ as compared to 5 keV SF5+, thus allowing for increased amounts of material to be removed prior to the approach of the gel point of the PMMA (dose at which a 3-D cross-linked structure is formed). Despite these increased erosion depths, the 8 keV SF5+ beam imparts greater initial structural damage, as indicated by decreased C═O contents in the C1s XPS spectra and increased amounts of graphitic type peaks in the corresponding SIMS spectra. Overall, the results indicate that, for thicker samples, one should employ higher beam energies for optimum results. However, for thinner films, in which the gel effect does not play a significant role, lower beam energies are preferred.

A cryogenic electrostatic trap for long-time storage of keV ion beams

We report on the realization and operation of a fast ion beam trap of the linear electrostatic type employing liquid helium cooling to reach extremely low blackbody radiation temperature and residual gas density and, hence, long storage times of more than 5 min which are unprecedented for keV ion beams. Inside a beam pipe that can be cooled to temperatures <15 K, with 1.8 K reached in some locations, an ion beam pulse can be stored at kinetic energies of 2-20 keV between two electrostatic mirrors. Along with an overview of the cryogenic trap design, we present a measurement of the residual gas density inside the trap resulting in only 2 x 10(3) cm(-3), which for a room temperature environment corresponds to a pressure in the 10(-14) mbar range. The device, called the cryogenic trap for fast ion beams, is now being used to investigate molecules and clusters at low temperatures, but has also served as a design prototype for the cryogenic heavy-ion storage ring currently under construction at the Max-Planck Institute for Nuclear Physics.

Two stage ion beam figuring and smoothening method for shape error correction of ULE® substrates of extreme ultraviolet lithography projection optics: Evaluation of high-spatial frequency roughness

The ULE® substrates used in projection optics of extreme ultraviolet lithography (EUVL) tools are mechanically prefinished with shape accuracy of several nanometer rms (specification: under 0.15 nm rms) with high-spatial frequency roughness (HSFR) (spatial wavelength: under 1 μm) of 0.06 nm rms. The ion beam figuring is used for the final shape error correction of the substrates at low spatial wavelength of greater than 1 mm using high energy (5–10 keV) Ar+ ion beam with 1 mm beam diameter. However, the surface roughness values of the ULE® substrates when machined by 5 and 10 keV Ar+ ion beams result in 0.15 and 0.17 nm rms, respectively; also it is to be noted that these values are greater than the required 0.15 nm rms specification of HFSR. Therefore, the authors developed a method where low energy (0.3 and 0.5 keV) ion beams are used for smoothening the surface of ULE® substrates, previously treated with high energy (5 and 10 keV) ion beams for figuring. By this two-stage operation of ion beam figuring and followed by smoothening, ULE® substrates with HSFR of 0.1 nm rms were obtained. Therefore, the authors conclude that the method presented here is one of the most effective methods for the figure error correction of ULE® substrate and will be useful in EUVL projection optics.

Ion beam sharpening of diamond tools having small apex angle without facet and ripple formations

The sharpening of diamond tools with small apex angles by low energy (1.0 keV) ion beam faces great challenges because of facet formation at the cutting edge of the tools. Adding to the problem is the formation of ripple, also appearing at the cutting edge of the tools that occurs when the ion beam bombardment is done at some off-normal angle of incidence. In this work, the authors investigated the dependence of the facet angles on the ion beam energy. They also studied the phenomenon of ripple formation as influenced by ion dose, ion beam energy, and ion incidence angles. Based on the experimental results they then developed a method for sharpening the tool with 45° apex without facet formation. They also studied ripple formation using 1.0 keV Ar+ ion beam at a tilt angle β of 30°. The work also used simulations to predict the changes in the profile of diamond tools during ion beam machining at a fixed tilt angle β. They found that simulation results on the profile of the diamond knife matched quite well with the experimental results. They conclude that it is possible to make sharp diamond knife with an apex angle of 45° and that sharpening time can be predicted applying simulations.

The kick-out mass selection technique for ions stored in an Electrostatic Ion Beam Trap

A simple mass selection technique which allows one to clean a keV ion beam of undesirable masses while stored in an Electrostatic Ion Beam Trap (EIBT) is described. The technique is based on the time-of-flight principle and takes advantage of the long storage times and self-bunching that are possible in this type of traps (self bunching being the effect that keeps ions of the same mass bunched in spite of their finite distributions of velocities and trajectories). As the oscillation period is proportional to the square root of the ion mass, bunches containing ions of different masses will separate in space with increasing storage time and can be kicked out by a pulsed deflector mounted inside the trap. A mass selector of this type has been implemented successfully in an EIBT connected to an Even-Lavie supersonic expansion source and is routinely used in ongoing cluster experiments.

Experimental characterization of the metastableD2−ion by photofragment imaging

The rovibrational states of the metastable anionic hydrogen molecule $\text{D}_{2}{}^{\ensuremath{-}}$ were studied in photofragmentation experiments at 532 nm employing a fast (keV) ion beam. By a three-dimensional fragment momentum imaging technique, the photodetachment and the dissociation of the system into neutral atoms were investigated at different times after production of the molecular ions. The present data are sensitive to both the rotational states and the vibrational wave functions of the anions and suggest that the level of rotational excitation, while still exceptionally high, is somewhat lower than estimated in recent theoretical predictions.

ZnO thin films deposited by capillaritron ion beam sputtering deposition

ZnO thin films were deposited by capillaritron ion beam sputtering deposition. The crystalline quality, stoichiometry and photoluminescence properties of as-deposited and annealed ZnO thin films were studied. The as-deposited ZnO films show no preferred crystallographic orientations while annealed films exhibit a strong single ZnO (0 0 2) diffraction peak at 34.50°. The stoichiometry of ZnO films were found to be dependent on both beam energy and annealing conditions that the atomic percent ratio of Zn/O can be controlled between 0.95 and 1.10. ZnO films deposited with 4 keV ion beam and annealed at 800 °C in oxygen shows the lowest defect related deep level visible emission, while 80% of oxygen atoms are still located in fully oxidized stoichiometric ZnO matrixes.

Study of formation of Cu nanoparticle using Swift heavy ions

In this paper, we present the use of keV and MeV ion beam irradiations and post-irradiation annealing to form Cu nanoparticles in fused silica glass. The sequence of process being: low energy irradiation of fused silica substrate, Cu thin film coating, SHI irradiation and annealing. Fused silica substrates were irradiated using 30 keV argon ions at fluences of 1 × 10 17 ion/cm 2. 10 nm Cu films were deposited on the low energy irradiated fused silica. These thin films coated fused silica samples were then irradiated using 120 MeV Ag 9+ ions at fluences ranging from 4 × 10 13 to 1 × 10 14 ion/cm 2. The irradiated samples were subjected to isochronal annealing in argon gas flow from 400 K to 1200 K for 30 min. The average sizes of Cu nanoparticles were estimated from optical absorption spectra using Mie's theory. The sizes of the Cu nanoparticles were also confirmed from GAXRD and TEM measurements. Post-irradiation annealing results indicate that the formation of Cu 3 nanocluster is favored at annealing temperature of about 700 K. High temperature annealing at 1200 K causes the formation of Cu 4 clusters as well as Cu nanoparticles (larger clusters). After annealing at 1200 K, for the sample 120 MeV Ag 9+ irradiated with high dose (1 × 10 14 ion/cm 2) only Cu nanoparticles are formed. The study suggests that irradiation induced defects provide nucleation sites for the formation of nanoparticles, latent tracks provide fast diffusion channels for Cu and, annealing provides required energy for the diffusion.

Assessment of surface damage and sidewall implantation in AlGaN-based high electron mobility transistor devices caused during focused-ion-beam milling

The surface amorphization and ion implantation in AlGaN-based high electron mobility transistor (HEMT) model structures caused by ionized gallium during focused-ion-beam milling have been investigated. The extent of Ga+ surface implantation likely to occur during deposition of the surface Pt protective layer was simulated for 30, 5, and 2 keV ion beams. Electron-transparent cross sections of AlGaN/GaN and AlGaN/AlN/GaN HEMT structures were then prepared for electron microscope observation using a dual-beam focused-ion-beam instrument operated at different beam energies. Experimental studies revealed that the upper 9 nm of the AlGaN layer had been amorphized during Pt deposition. Nanoprobe x-ray microanalysis confirmed intermixing with Pt as well as implantation of Ga ions into the upper regions of the foil. Deposition of the first few hundred nanometers of Pt using an electron beam, rather than the usual Ga+ beam, enabled surface damage and ion implantation to be completely avoided. Sidewall damage for specially prepared cross sections was assessed from bright-field and high-angle annular-dark-field images. For final membrane thinning at 30, 5, and 2 keV, the thicknesses of visibly damaged layers were approximately 20, 8, and 4 nm, respectively, roughly twice as large as predicted by simulations.

Study of formation of Cu nanoparticle using Swift heavy ions

Abstract In this paper, we present the use of keV and MeV ion beam irradiations and post-irradiation annealing to form Cu nanoparticles in fused silica glass. The sequence of process being: low energy irradiation of fused silica substrate, Cu thin film coating, SHI irradiation and annealing. Fused silica substrates were irradiated using 30 keV argon ions at fluences of 1 × 10 17 ion/cm 2 . 10 nm Cu films were deposited on the low energy irradiated fused silica. These thin films coated fused silica samples were then irradiated using 120 MeV Ag 9+ ions at fluences ranging from 4 × 10 13 to 1 × 10 14 ion/cm 2 . The irradiated samples were subjected to isochronal annealing in argon gas flow from 400 K to 1200 K for 30 min. The average sizes of Cu nanoparticles were estimated from optical absorption spectra using Mie's theory. The sizes of the Cu nanoparticles were also confirmed from GAXRD and TEM measurements. Post-irradiation annealing results indicate that the formation of Cu 3 nanocluster is favored at annealing temperature of about 700 K. High temperature annealing at 1200 K causes the formation of Cu 4 clusters as well as Cu nanoparticles (larger clusters). After annealing at 1200 K, for the sample 120 MeV Ag 9+ irradiated with high dose (1 × 10 14 ion/cm 2 ) only Cu nanoparticles are formed. The study suggests that irradiation induced defects provide nucleation sites for the formation of nanoparticles, latent tracks provide fast diffusion channels for Cu and, annealing provides required energy for the diffusion.

Microwave power absorption coefficient of an ECR xenon ion thruster

A 20-cm diameter xenon ion thruster with electron cyclotron resonance (ECR) discharge generates 30 mN of thrust at a total electric power consumption of 1 kW for spacecraft propulsion by ejecting 1.1 keV ion beam. By optimizing the discharge chamber length, magnetic field and propellant flow injection, ion beam currents of 500 mA at a microwave power of 100 W had been obtained at a frequency of 4.25 GHz with SmCo magnets arranged on a flat discharge chamber. The performance was highly dependent on the propellant injection method that affects electron-heating process. Two-dimensional microwave E-field distributions inside the discharge chamber were experimentally investigated for the best and the worst injector layouts. Microwave power absorption coefficient was estimated using the E-field distributions with and without plasma discharge. The coefficient decreases as the microwave power decreases and electron density gets close to an ECR cutoff density in all cases. The worst injector layout showed larger reflection and smaller absorption coefficient even at small beam currents. In the best configuration, microwave reflection was sufficiently smaller than 10% and 70–90% of the microwave power launched into the discharge chamber was absorbed by plasma electrons.

Fast-ion-beam laser-induced-fluorescence measurements of branching fractions and oscillator strengths in Nd II

We measured the spontaneous-emission branching fractions of 46 levels in Nd II, selectively populated via single-frequency laser excitation of a 10 keV ion beam. The levels studied had term energies up to 29 955 cm–1, and decay branches with spontaneous emission in the range 372–850 nm were detected. The experimental accuracy for branching fractions over 0.1 was ~7%. We used these branching fractions along with our previously determined radiative lifetimes to infer transition probabilities and oscillator strengths for 430 transitions, which are useful for stellar abundance determinations. PACS Nos.: 32.70Cs, 95.30Ky

Nonlinear optical properties of MeV and keV ion beam synthesized Ag nanoclusters

Ag nanoclusters embedded in silica glass matrix have been synthesized by high fluence ion implantation using both keV and MeV ion beams. In keV implantation case, optical absorption shows an intense surface plasmon resonance (SPR) peak corresponding to the Ag clusters formed in the matrix. Transmission electron microscopy (TEM) measurements carried out on identically implanted SiO2 thin films on a TEM catcher grid shows the presence of Ag nanoclusters of size around 4nm in the matrix. However, for the MeV implantation case, the SPR peak appears in the optical absorption spectra only after air annealing the sample at 500°C for one hour. For the annealed samples, TEM measurements show the presence of 6nm sized Ag nanoclusters. On the other hand the as-implanted sample shows smaller nanoclusters with a lower particle density in the matrix. Interestingly, open aperture z-scan measurements carried out on keV implanted samples did not show any nonlinear absorption, while the MeV as-implanted as well as annealed samples showed nonlinear absorption. The nonlinear absorption coefficient of the MeV annealed sample is extracted from a fit to the z-scan data considering a three photon like absorption process.

An electrostatic deflection system

The system for electrostatic deflection of high-energy (up to 10 keV) ion beams at large (up to 7°) angles contains a dodecapole assembly consisting of 12 electrodes and a two-channel deflection voltage source. Each channel generates two voltages symmetrically changing from −600 to +600 V with respect to the ground, and, in this case, the absolute values of the both voltages differ by ≤1 V. The temperature voltage drift is ≤50 ppm/°C. Output voltage levels are set by a 16-bit digital-to-analog converter. The deflection-voltage source is a 95 × 65 × 40-mm module.